Mystery of turtles’ voyage uncovered by UNC biologists

Research published by UNC biologists Thursday revealed sea turtles’ secrets to navigating the ocean and returning home.

The endangered loggerhead sea turtle travels completely around the Atlantic Ocean during its lifetime, beginning along the eastern coast of Florida and passing by Spain, Portugal and the northern coast of Africa, biology professor Kenneth Lohmann said.

The loggerhead is only able to make this five to 10 year journey once in its lifetime, but it returns to its original home using imprinting and magnetic fields as a sort of global positioning system.

Imprinting is crucial to turtles being able to find their birthplaces, J. Roger Brothers, a Ph.D. student in the biology department, said.

“Imprinting is really just a special form of learning,” Brothers said. “So we usually think of imprinting in terms of geese imprinting on their mother figure.”

Brothers said the earth’s magnetic field is useful for two reasons.

“The first is that it’s different everywhere in the world. And the second is it exists everywhere in the world,” he said.

“So even out in the middle of the ocean, where turtles migrate, where it seems very featureless — if you’ve ever been out on a boat, there’s nothing to tell you were you are — turtles can sense the earth’s magnetic field and they’ve developed this way to use the earth’s magnetic field almost like an internal GPS.”

The biology department’s research has solved the mystery of sea turtle navigation, but with magnetic fields at risk from beach development, the turtles are at risk, too.

“People don’t usually think much about magnetic field distortions when hotels are built on beaches,” Lohmann said. “Between that and the wire cages that are sometimes put over the turtle nests to protect them from predators, it’s likely that we’ve been disrupting the magnetic environment ... that may actually impair their ability to return to their home beaches.”

Bald Head Island Conservancy Executive Director Suzanne Dorsey said they currently protect the nesting grounds with a wire cage.

The UNC study included a large portion of data conducted by the state of Florida, but in the more recent studies behavioral experiments have been conducted on turtles housed in a lab in Wilson Hall.

To monitor the turtles’ directional instincts, UNC biologists strap the turtles into cloth harnesses and lower them into containers of water that are surrounded by machines that simulate the regional magnetic fields researchers want to study.

The turtles are unaware they’re swimming in place, but they still swim in the same direction as turtles following the Atlantic loop.

“To me, it is just one of the great wonders of the natural world — how something like a baby sea turtle can enter the ocean and literally swim across the Atlantic Ocean and somehow return to the same area of coastline where it started out,” Lohmann said. “That’s an astonishing navigational ability.”

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